How to access BIOS memory?

I have several Dell computers with a LCD display in front of. The displayed string can be changed from BIOS itself, but I want to modify it from within the OS.
I checked the CMOS memory (using port 0x70/71) but this information is not visible here (I tried to change the string and then check for changes).
I also checked the memory to see if the configuration is mapped somewhere, but I cannot find anything.

So, does someone knows where BIOS maps its additionnal memory, or how to access it if it is port-based access (like basic CMOS).

Ho, and I checked existing tools to change the configuration. Tools are able to change basic configuration elements (such as activate numlock and many others) but are not able to handle these LCD strings.